In DT3, I can open a floating info panel as before in DT2, with shortcut command-shift-I.
Unlike before, the same shortcut doesn’t put it away again. Or rather, it does, but it immediately reappears. I have to click elsewhere in the window (or any DT3-occupied part of the screen) to make it go away. I assume (and hope) the previous behaviour was intended.
Contrary to version 2 it’s not a floating panel, therefore Cmd-Shift-I just opens the popover. But Esc can be used to close it.
You’re correct, I meant the popover. And the escape to close works.
In that case it’s not a bug, but a minor quibble: this shortcut used to be a toggle – my fingers clearly remember it as such 
and it takes less thinking and moving-around-fingers to close an item like that with the same shortcut that opened it. As is the case with show/hide the inspectors, for instance.
3.0.2 will improve this.